大型海岸海洋結構附近波浪之影像量測

本研究以雙眼系統為架構，架設兩台攝影機，拍攝大型結構物如圓柱、船舶、離岸潛堤等附近流場的動態波浪影像，並進行運算，做三維重建。本文以直接線性轉換法為理論基礎，配合內部校正、外部校正、影像糾正及正規化相關法，進行影像匹配分析與立體影像之重建，再與波高計進行比對分析誤差。為解決在實驗水槽波紋不明顯，造成無特徵點的現象，在此提出多種實驗方法，強制實驗水槽水面有特徵點，使匹配成功率提高，更使重建影像與波高計比對的誤差減少，此外在擷取影像速率也有提升，圖像匹配的運算速率亦加快。整體而言，立體影像與波高計量測比對良好，可以取代實驗水槽傳統波浪量測方式，亦可輕易求取結構物附近大範圍的波場資訊。

關鍵字

立體影像；極線幾何；影像糾正

並列摘要

A binocular stereo imaging system is used to retrieve water surface elevation fields around large fixed ocean structures such as cylinder, ship and submerged breakwater. Two spatially offset CCD cameras with overlapping fields of view are synchronized for data acquisition. Direct linear transformation based on perspective projection of pinhole camera is used to transform between the image and the world coordinates. A two-step calibration technique is used to determine the intrinsic and extrinsic camera parameters. Epipolar geometry and normalized cross correlation methods are used for image matching and reconstruction of 3D water surface profiles. Image rectification method is employed which fits both images in the same rectified plane parallel with the cameras' baseline. This rectification process creates parallel epipolar lines that constrain the correlation process, thus reducing the computational effort. Reconstruction of 3D water surface profiles are then compared with in-situ wave gauge measurements. To increase the number of identifiable features and textures between the stereo image pair, both surface bubble technique and projecting a structured lighting pattern on the water surface technique are employed. These techniques increase the success rates of image matching and also decrease the errors between image and wave gauge measurements. Overall comparisons between image and wave gauge measurements are very good, which indicates that this image technique is applicable for measuring water surface wave fields around ocean structures.

並列關鍵字

stereo image ； Epipolar geometry ； image rectification

國際替代計量

大型海岸海洋結構附近波浪之影像量測

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